docs: def is_config_var(var):
      """ Checks if the given value is a valid ``file_config.var``.
  
      :param var: The value to check
      :return: True if the given value is a var, otherwise False
      :rtype: bool
      """
  
      return (
          isinstance(var, (attr._make.Attribute, attr._make._CountingAttr))
          and hasattr(var, "metadata")
          and CONFIG_KEY in var.metadata
      )